1 64 COMPARATIVE ANATOMY 



sperm-sac when it has absorbed all the available nourish- 

 ment. 



In the reproductive phase of the life cycle, which is practic- 

 ally identical in the two species under consideration, three 

 distinct events may be recognised. Firstly, there is the associa- 



F. 



Kg. 34- 



A, the eight sporozoites, s^z, of Monocystis escaping from the Sporo- 

 cyst. J3, a young trophozoite lodged in the centre of a sperm-morula 

 of the earthworm ; tr, trophozoite ; j/, sperm-mother cells. C, a free 

 individual of M. agilis, with a few withered sperm cells adhering to it. 

 Z>, a mature individual of M. magna attached to sf, the sperm funnel 

 of an earthworm. , two mature individuals of M, ina.gna )o'mz& in 

 "association." F, the two associates have become hemispherical and 

 have formed a cyst ; ep, epicyst ; en, endocyst. G, a section through 

 two encysted associates snowing nuclear division in progress; ky, a 

 degenerating karyosome ; mit t a much elongated mitotic spindle of a 

 dividing nucleus; ', resting nucleus preparing for division. (A-C, 

 original ; D-G after Cu^enot. A is purely schematic, the liberation of 

 the sporozoites not having been actually observed in MonocystisC) 



tion and enclosure in a common cyst-wall of two mature 

 trophozoites, a process which must by no means be confounded 

 with conjugation. Secondly, there is the subdivision of the 



